Remotely Controlled Micromanipulation by ... - ACS Publications

Subscriber access provided by EPFL | Scientific Information and Libraries

Article 3

4

Remotely Controlled Micromanipulation by Buckling Instabilities in FeO Nanoparticle Embedded Poly(N-isopropylacrylamide) Surface Arrays Vinicio Carias, Zohreh Nemati Porshokouh, Kristen Stojak Repa, Javier Alonso, Hariharan Srikanth, Jürgen Rühe, Ryan Toomey, and Jing Wang

ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05899 • Publication Date (Web): 20 Sep 2016 Downloaded from http://pubs.acs.org on September 20, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Remotely Controlled Micromanipulation by Buckling Instabilities in Fe3O4 Nanoparticle Embedded Poly(N-isopropylacrylamide) Surface Arrays Vinicio Carias,a,c Zohreh Nemati Porshokouh,b Kristen Stojak Repa,b Javier Alonso,b,e Hariharan Srikanth,b Jürgen Rühe,c Ryan Toomey,a* and Jing Wangd* a

Department of Chemical & Biomedical Engineering, University of South Florida, 4202 E. Fowler Ave., Tampa, FL 33620 USA. b Department of Physics, University of South Florida, 4202 E. Fowler Ave., Tampa, FL 33620, USA c

Department of Microsystems Engineering - IMTEK, University of Freiburg, Georger-Köhler-Allee 103, 79110 Freiburg, Germany d

Department of Electrical Engineering, University of South Florida, 4202 E. Fowler Ave., Tampa, FL 33620, USA

e

BCMaterials Edificio No. 500, Parque Tecnológico de Vizcaya, Derio, 48940 Spain

ABSTRACT: The micromanipulation of biological samples is important for microbiology, pharmaceutical science, and related bio-engineering fields. In this work, we report the fabrication and characterization of surface-attached microbeam arrays of 20 µm width and 25 µm height made of poly(Nisopropylacrylamide), a thermoresponsive polymer, with embedded spherical or octopod Fe3O4 nanoparticles. Below 32 °C, the microbeams imbibe water and buckle with an amplitude of approximately 20 µm. Turning on an AC-magnetic field induces the microbeam array to expel water due to the heating effect of the nanoparticles (magnetic hyperthermia), leading to a reversible transition from a buckled to nonbuckled state. It is observed that the octopod nanoparticles have a 30% greater heating rate (specific absorption rate, SAR) than the spherical nanoparticles, which shortens the time scale of the transition from the buckled and non-buckled state. The return of the microbeams to the buckled state is accomplished by turning off the AC magnetic field, the rate of which is dictated by dissipation of heat and is independent of the type of nanoparticle. It is further demonstrated that this transition can be used to propel 50 µm spherical objects along a surface. While the motion is random, this study shows the promise of harnessing shape-shifting patterns in microfluidics for object manipulation. Keywords: AC Magnetic Hyperthermia, Magnetic Thermoresponsive Materials, Poly(N-isopropylacrylamide), Buckling, Lower Critical Solution Temperature

INTRODUCTION The ability to manipulate micrometer or nanometer scale analytes and objects in a well-controlled manner has been central to the successful implementation of microfluidic1-2 and lab-on-a-chip3-4 applications within the last decade.5-7 Some of the current stateof-the-art technologies include micro-grippers,8 optical tweezers,911 magnetic tweezers,12-13 opto-thermocapillary manipulators,

dielectrophoretic manipulations, surface acoustic wave (SAW) acoustophoresis, and micro-robots.14-16 Generally, such technologies are expensive and difficult to implement in microfluidics. In this study, we investigate topography (or shape) shifting surfaces based on surface-attached microbeams of cross-linked poly(N-isopropylacrylamide), or PNIPAAm,-magnetite composites in order to manipulate the movement of micron-sized particles. PNIPAAm is a well-known thermally responsive polymer17 18 that abruptly changes solubility in water at the so-called volume phase transition temperature (VPTT), which is roughly 32˚C.19-20 Cross-linked networks of PNIPAAm swell with water below 32˚C and force water out above 32˚C, providing an actuation mechanism that is entirely built at the material level without the need for external electronics. Other environmental cues that have been used to trigger the aforementioned abrupt and reversible hydrophilic/hydrophobic transition include light21, ionic strength22, pH23, electric field24, and magnetic field25. In this study, AC magnetic fields were used to induce heating (magnetic hyperthermia) in composite PNIPAAm/magnetite-nanoparticle microbeams, causing the microbeams to reversibly switch from a buckled to a non-bucked state26-27 depending on whether the magnetic field is turned on or off (as shown in Figure 1). Such a strategy has previously been used in magnegic PNIPAAm microgels to control both diameter28 and aspect ratio29, as well for ondemand30 and pulsatile drug delivery31. In the current study, the buckling, or shape-shift, of a microbeam arises by chemically linking, or attaching, the PNIPAAm to the underlying surface. At temperatures where the PNIPAAm rejects water, the structure takes on the shape of a columnar beam. At temperatures where PNIPAAm imbibes water, surface-attachment prevents swelling along the length of the beam, which builds up a compressive stress that is partially relieved through a physical distortion of the beam. This approach can be used to either move objects in a controlled manner, or to develop active antifouling surfaces.

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 7

loops were measured at room temperature (300K) in applied fields up to 50 kOe.

Figure 1. Conceptual schematic diagram showing the PNIPAAmFe3O4 hydrogel microbeams that buckle when exposed to water and straighten, due to its abrupt volumetric phase transition, when exposed to an AC magnetic field (AMF). Important aspects of using magnetic fields to induce a shape shift in the composite gels concerns the heating efficiency of the embedded nanoparticles as well as the rate at which the transition from one state to another takes place. To address heating efficiency, several strategies have been proposed in the last few years, including varying size, saturation magnetization and effective anisotropy of the nanoparticles.32-33 Specifically, it has been shown that by changing the shape of the nanoparticles, for example from spherical to cubic shape, the surface anisotropy increases and so does their heating efficiency or specific absorption rate (SAR).34-35 Towards this end, this work compares the microfabrication of surface-attached PNIPAAm microbeams with both embedded spherical and highly anisotropic octopod Fe3O4 nanoparticles. Our group has previously shown that nano-octopods36 have higher hysteresis losses (heating efficiency), especially in the high field region than spherical particles, potentially leading to faster response of the PNIPAAm microbeams.

EXPERIMENTAL SECTION Materials. Spherical magnetite nanoparticles (Fe3O4, 99.5%, 25 nm) were acquired from Nanostructured & Amorphous Materials, Inc. The materials used for and synthesis procedure of the Fe3O4 nano-octopods were reported previously.36,37 For the bead movement studies, 50 µm-diameter NIST NT34N traceable polystyrene particles were obtained from Bangs Laboratories, Inc. For polymer synthesis, N-Isopropylacrylamide (NIPAAm), N, N’methylenebisacrylamide (MBAm), 2,2-dimethoxy-2phenylacetophenone (DMPA), 3-(trichlorosilyl)propyl methacrylate (TPM), acetone, heptane, and hexane were all obtained from Sigma-Aldrich. For fabrication of the polymer arrays, polydimethylsiloxane (PDMS) SYLGARD® 184 silicone elastomer kit was acquired from Dow Corning. SU-8 2035 photoresist and OmniCoat were purchased from MicroChem. Instruments. The fabrication of a SU-8 master mold was performed through standard UV lithography with the use of a Laurell WS-650MZ-23NPP spin coater and an EVG®620 contact mask aligner calibrated by a Karl Suss 100S optical power meter.

The evaluation of heating efficiency for both types of Fe3O4 nanoparticles and the hyperthermia experiments were conducted under an AC magnetic field (0–800 Oe) at 310 kHz, by using a 4.2 kW EASYHEAT LI 3542 precision induction heating system equipped with an eight-turn helical coil with a diameter of 25 mm and a length of 43 mm. The measurements were performed in water with suspended nanoparticles at 2 mg/ml of concentration through calorimetric methods, using a fiber optic probe to record the increase in temperature, while applying the AC magnetic field. Cooling water was continuously circulated through the coil to keep it refrigerated. The surface-attached PNIPAAm-Fe3O4 nanocomposite-based microfluidic manipulators were placed at the center of the coil, where the AC magnetic field reached its maximum magnetic field strength of 800 Oe. An Agilent U5855A TrueIR Thermal Imager was used to obtain IR thermal images (320 x 240 resolution) of the nanoparticle embedded surface arrays. The IR images were taken at different zoom modes, including digital zooms of 80x and 160x magnification. Preparation of PNIPAAm-Fe3O4 Composite Microbeams. PNIPAAm-Fe3O4 polymer nanocomposite microfluidic manipulators that consist of an array of surface-attached parallel microbeams of 20µm (width) x 25 µm (height) x 5 mm (length) were fabricated by following a soft lithography process, as previously described.26, 38-39 The glass coverslip was surface treated with a 3(Trichlorosilyl)propyl methacrylate (TPM) monolayer to form a covalent bond between it and the molded PDMS channels.40 First, the coverslip was treated with an O2 plasma (6.8W and 500mTorr) for 15 minutes. Second, the coverslip was immersed in a 1mM TPM solution in a 4:1 mixture of heptane and tetrachloride as the solvent, and then rinsed in hexane and deionized water. The surface treatment was carried out in an oxygen-free (N2) environment at room temperature. Soft lithography, particularly the procedures based on micromolding in capillaries (MIMIC), was employed to fabricate the magnetic hydrogel based microbeam micromanipulators. A PDMS stamp was placed onto a TPM treated glass slide with the relief facing the substrate to form microcapillaries, which absorbed a magnetic NIPAAm acetone solution containing 5 mg/ml MBAm (crosslinker), 20 mg/ml DMPA (photo initiator), 25 mg/ml Fe3O4 nanoparticles, and 200 mg/ml NIPAAm through capillary action. Once the microcapillaries were filled, the magnetic NIPAAm polymerization was initiated with a 365-nm ultraviolet light for 4 minutes, followed by the removal of the PDMS stamp, leaving behind the patterned and surface-attached PNIPAAm-Fe3O4 microbeam micromanipulators.

The sample images were taken with an AmScope SM-4TY-FRL professional trinocular stereo zoom microscope and an AmScope MU1400 14MP microscope digital camera. An FEI Morgagni 268 transmission electron microscope (TEM), operating at 60 kV, was used to characterize the size, crystallinity, and homogeneity of the magnetite nanoparticles. The magnetic properties were measured using a physical property measurement system (PPMS) by Quantum Design, with a vibrating sample magnetometer (VSM) option. The magnetic hysteresis

Figure 2. SEM images of magnetite nanoparticles showing the size, shape and size distribution of (a) the synthesized nanooctopods, and (b) commercial iron oxide nanospheres.


Page 3 of 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


RESULTS AND DISCUSSION Various experiments were performed to compare the hyperthermia heating efficiency of the commercial Fe3O4 nanospheres and the in-house synthesized Fe3O4 nano-octopods, which have been previously reported36. The heating efficiency is instrumental to the overall characteristic behavior, such as response time, of the magnetic hydrogel microactuators. The commercial Fe3O4 nanoparticles have been known for their good magnetic properties for hyperthermia applications.31 However, due to their unique surface anisotropy, the synthesized Fe3O4 nano-octopods are anticipated to have even better heating efficiency and hyperthermia properties, thus showing a superior micromanipulator device performance, e.g., the response time.

lapsed state (Figure 3). It only took 40 seconds for the equivalent microbeam with the nano-octopods to reach the collapsed state (Figure 4). The buckle amplitude of the microbeams upon turning on the magnetic field is shown in Figure 5. Interestingly, it can be seen that the microbeam with the embedded nano-octopods transitions quite rapidly (20 seconds) between the buckled and collapsed states in the presence of the magnetic field, whereas the transition occurs in approximately 60 seconds for the microbeam with the nanospheres.

Figure 2 presents images of the synthesized Fe3O4 nano-octopods and the commercial nanospheres, respectively. The nano-octopods show a slightly deformed characteristic cubic shape. As inferred from the inset, the synthesized magnetite octopods also exhibit a relatively narrow size distribution (D = 47.4 nm and σ = 4.6 nm), which is of utmost importance to achieve a homogeneous and optimized response. As compared to the commercial nanoparticles (D = 29.1 nm and σ = 8.1 nm), it is evident that the synthesized nano-octopods possess an appreciably narrower size distribution. For comparison purposes, PNIPAAm microbeams were fabricated while embedded with the commercial nanospheres or the synthesized nano-octopods, both at a 10 wt% concentration. A time series of microscopy images of a single microbeam with either the nanospheres (Figure 3) or nano-octopods (Figure 4) show the response of each microbeam with respect to the AC field for up to 140 seconds. Initially, the dry PNIPAAm-Fe3O4 hydrogel microbeams were exposed to water resulting in a buckled state. In this state, the nanosphere microbeams have an average buckle amplitude (measured from the centerline of the beam) of 19 µm +/- 10% and the nano-octopod microbeams have an average buckle amplitude of 23 µm +/- 10%.

Figure 3. Time-lapse, top-view microscope image sequences of a magnetic hydrogel microbeam filled with 10 wt% Fe3O4 commercial nanospheres as it gradually collapses under an 800 Oe and 310 kHz magnetic field. In both cases, at time zero, a 310 KHz magnetic field of 800 Oe was turned on. While it took approximately 80 seconds for the hydrogel microbeam with the nanospheres to reach a fully col-

Figure 4. Time-lapse, top-view microscope image sequences of a magnetic hydrogel microbeam filled with 10 wt% Fe3O4 nanooctopods as it gradually collapses under an 800 Oe and 310 kHz magnetic field.

Figure 5. Time evolution of the buckling amplitude of the magnetic PNIPAAm microbeams under an 800 Oe and 310 kHz magnetic field. In order to interpret these results, Fig. 6 shows IR thermography readings of the microbeams with both the nanospheres and the nano-octopods exposed to a field of 800 Oe. Both are single run experiments, with readings taken at the center of the microbeam array. The repeatability of this measurement was approximately +/- 1 °C. In order to minimize error in the individual readings, the



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

temperature heating curves (expressed as a change in temperature ∆T) were fit to the following form41: ∆ ∆ 1 exp

(1)

Where ∆Tmax and τ represent the maximum temperature increase and a characteristic heating time, respectively. In the case of the nanospheres, ∆Tmax = 17 °C and the initial heating rate (∆Tmax /τ ) of the microbeams was 0.19 °C per second. In the case of the nano-octopods, ∆Tmax = 29 °C and the initial heating rate (∆Tmax /τ ) of the microbeams was 0.25 °C per second.

Page 4 of 7

After cessation of the magnetic field, both microbeams return to the buckled state. Figure 8 shows the time series of microscopy images for both the nanosphere and nano-octopod embedded microbeams. Time zero is chosen at the first point the beams start to swell (indicating the temperature is nearing the transition temperature). In contrast to the magnetic hyperthermia response of the microbeams, the time scale of reswelling is approximately the same for both types of nanoparticles, recovering the initial buckle amplitude in about 1 minute. This is consistent with the notion that reswelling is controlled by heat dissipation from the system. As long the external temperature and the volume of water is the same between the two systems, the reswelling kinetics should also be similar. This is further exemplified in Figure 9, which shows the buckle amplitude of both microbeams as a function of reswelling time.

Figure 6. Comparison of the measured temperature increase of the magnetic PNIPAAm microbeams when exposed to an AC magnetic field of 800 Oe at a frequency of 310 kHz by using IR thermography. The error bars represent a precision of +/- 1 °C. Using the results of fitted thermal measurements, Figure 7 reveals the deformation amplitude as a function of the change in temperature, where it can now be observed that the collapse of the beam displays similar behavior for both types of nanoparticles within the precision of the measurements. In both cases, room temperature was 24 °C. The collapse started at 29 +/- 1 °C and was complete by 33 +/- 1 °C, independent of the type of the nanoparticle.

Figure 7. Temperature evolution of the buckling amplitude of the magnetic PNIPAAm microbeams under an 800 Oe and 310 kHz magnetic field.

Figure 8. Time-lapse, top-view microscope image sequences of a magnetic hydrogel microbeam filled with (a) 10 wt% Fe3O4 nanooctopods and (b) 10 wt% FeeO4 nanospheres after cessation of the magnetic field. Time zero is taken at the point where reswelling starts to occur.

Figure 9. Temperature evolution of the buckling amplitude of the magnetic PNIPAAm microbeams upon reswellling after cessation of the magnetic field. In order to better understand the differences in the magnetic hyperthermia of both nanoparticles, we measured the DC magnetic


Page 5 of 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


hysteresis loops at room temperature and the heating curves for both types of nanoparticles (see Supplementary Information). Essentially, the nano-octopods present bigger hysteresis loop area, which indicates greater hysteresis losses and better heating capacity (Figure S1). This is confirmed by the heating curves and extracted heating efficiency or SAR values for both samples at different fields. At 800 Oe, the SAR is around 30% larger for the nano-octopods than the commercially available nanospheres. This value of 30% is also consistent with the initial heating rates of the nanoparticles in the microbeams, as measured and reported in Figure 5. This is significant in the sense that the PNIPAAm gel does not appreciably alter the heating characteristics of the nanoparticles.

Figure 10 shows zoomed-in optical images (with respect to Figure 3 and 4) of the swollen, buckled microbeams at time zero. The optical images reveal that the nanospheres are irregularly dispersed in the microbeams whereas the nano-octopods are much more uniformly dispersed. Remarkably, while this difference in dispersion has a negligible effect on the swelling kinetics, it may have some effect on the wavelength of the buckle and amplitude.

In order to demonstrate the capabilities of remotely-controlled micromanipulation of the magnetic hydrogel microbeams, 50 µmdiameter polystyrene beads were adsorbed to a microarray surface. Figure 11 shows two optical images of the surface with the 50 µm particles moving as a result of the PNIPAAm-Fe3O4 nanooctopod microbeams transitioning between the buckled and collapsed states. To simplify visualization, 4 particles were chosen that were originally aligned (at 0 seconds) and highlighted by a single white line. Thirty seconds after the field is turned on, it is observed that the particles move out of alignment as a direct consequence of the change in amplitude of the buckled beams. This 30 second time frame is consistent with the time scale of the buckling amplitude change reported in Figure 7. In order to understand the significance of this motion over repeated transitions of the buckled/non-buckled transition, Figure 12 shows the movement map of 6 beads through a repeated cycling of magnetic field exposure. It is important to note that the buckling transition temperature and amplitude change is quite repeatable over many (>100) cycles of the AC field. The even numbers indicate when the magnetic field was on and the odd numbers indicate when the magnetic field was off. Each cycle was separated by 150 second intervals.

Figure 11. Movement of 50 µm-diameter polystyrene beads as the microbeams change shape from the buckled (at time = 0 seconds) to the non-buckled state (at time = 30 seconds) following the application of the AC magnetic field at 800 Oe and 310 kHz. Figure 10. Top-view microscope images of hydrogel micro-beam showing the wavelength for (a) the Fe3O4 nanospheres, and (b) the FeeO4 nano-octopods. Toward this end, Mora et al. investigated the buckling patterns developed by the swelling of soft gel microbeams.42 They applied a linear elastic model to buckling induced on polymer strips and determined that the first stable wavelength is: λ = 3.256h

(2)

where h is the height of the structure at the time of buckling. Early in the swelling process the height increases, until a critical compressive stress, beyond which buckling occurs. We have shown that microbeams comprised of pure PNIPAAm without added nanoparticles have a buckling wavelength between 110-125 µm.26 Interestingly, the microbeams with the nano-octopods follow this same trend with a wavelength of roughly 100 µm. The microbeams with the commercial nanospheres, on the other hand, have a lower wavelength of 80 µm, which is in line with the wavelength prediction for a height of 25 µm at the time of buckling. Hence, it can be surmised that the non-uniform distribution of the commercial nanospheres may lead to “frustrated” swelling and earlier onset of the instability leading to buckling. This also may explain why the buckle amplitude of the swollen nanosphere microbeams is slightly less than the nano-octopod beams, approximately 19 µm vs 23 µm, respectively.

While the bead movement is random, it is interesting to note that in 6 cycles of small shift (~20 µm) in the buckling amplitude, the microbeams can move the 50 µm beads anywhere from 5 µm to 200 µm in total distance from the original position. The maximum distance that a bead should travel (if the bead remains bound to the microbeam) is roughly the amplitude change of the buckle, or 20 µm. That said, the width of the beam also expands or contracts depending on whether the AC field is turned off or on, respectively, effectively shearing the bead from the surface. In areas of known defects of the microbeams, it was observed that the beads could travel significantly farther than 20 µm, perhaps due to a rolling or hopping mechanism. While an unintended finding in this study, it points to the notion that beam shape and size, if well controlled, could lead to precise control over the movement of the particles.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 7

acknowledges partial support from NSF CMMI-1143053. The authors acknowledge valuable discussions about the nanostructures and magnetic analysis with Dr. Manh-Huong Phan.

REFERENCES

Figure 12. Movement map of six 50 µm-diameter polystyrene beads through repeated cycling of magnetic field exposure over the nano-octopod filled microbeams. Even numbers indicate when the magnetic field was on and odd numbers indicate when the magnetic field was off.

CONCLUSIONS Although the bead movement is random in these studies, we have demonstrated the proof of concept of micromanipulation through fabricated surface attached magnetic hydrogel microbeams. It is anticipated through rational design of the geometry of the PNIPAAm structures that motion can be directed in carefully controlled directions. Furthermore, Fe3O4 nano-octopods have been synthesized and exhibited 30% better hyperthermia heating efficiency than commercial Fe3O4 nanoparticles, allowing a 2-3X faster unbuckling response of the embedded microbeams. This novel approach to fabrication of repeatable shape-changing micro-structures for micromanipulation triggered at the material level without the need for electronics is ideal for applications in microfluidics. Also, the ability to remotely modify surface geometries makes this system appealing for non-contact applications. Remotely controlled micromanipulation by an AC magnetic field can be achieved through a variation of micro-structure geometries and Fe3O4 nanoparticle concentrations.

AUTHOR INFORMATION Corresponding Author * [email protected]; [email protected]

Author Contributions The manuscript was written through contributions of all authors. / All authors have given approval to the final version of the manuscript.

SUPPORTING INFORMATION Room temperature DC magnetic hysteresis loops and SAR data are provided for the commercial nanoparticles and nano-octopods.

ACKNOWLEDGMENT Vinicio Carias acknowledges the German-American Fulbright Commission and the McKnight Dissertation Fellowship for the financial support required to complete this work. Javier Alonso acknowledges the financial support provided through a postdoctoral fellowship from Basque Government. Ryan Toomey

(1) Zhang, C.; Khoshmanesh, K.; Mitchell, A.; Kalantar-Zadeh, K., Dielectrophoresis for Manipulation of Micro/Nano Particles in Microfluidic Systems. Anal. Bioanal. Chem. 2010, 396, 401-420. (2) Ozkan, M.; Wang, M.; Ozkan, C.; Flynn, R.; Esener, S., Optical Manipulation of Objects and Biological Cells in Microfluidic Devices. Biomed. Microdevices 2003, 5, 61-67. (3) Medoro, G.; Manaresi, N.; Leonardi, A.; Altomare, L.; Tartagni, M.; Guerrieri, R., A Lab-on-a-Chip for Cell Detection and Manipulation. IEEE Sens. J. 2003, 3, 317-325. (4) Tanaka, Y.; Sato, K.; Shimizu, T.; Yamato, M.; Okano, T.; Kitamori, T., Biological Cells on Microchips: New Technologies and Applications. Biosens. Bioelectron. 2007, 23, 449-458. (5) Amato, I., Nanotechnologists Seek Biological Niches. Cell 2005, 123, 967-970. (6) Desai, J. P.; Pillarisetti, A.; Brooks, A. D., Engineering Approaches to Biomanipulation. Annu. Rev. Biomed. Eng. 2007, 9, 35-53. (7) Laval, J.-M.; Mazeran, P.-E.; Thomas, D., Nanobiotechnology and Its Role in the Development of New Analytical Devices. Analyst 2000, 125, 29-33. (8) Kim, D. H.; Kim, B.; Kang, H., Development of a Piezoelectric Polymer-Based Sensorized Microgripper for Microassembly and Micromanipulation. Microsyst. Technol. 2004, 10, 275-280. (9) Grier, D. G., A Revolution in Optical Manipulation. Nature 2003, 424, 810-816. (10) Ashkin, A.; Dziedzic, J. M.; Yamane, T., Optical Trapping and Manipulation of Single Cells Using Infrared Laser Beams. Nature 1987, 330, 769-771. (11) Jiang, Y.; Matsumoto, Y.; Hosokawa, Y.; Masuhara, H.; Oh, I., Trapping and Manipulation of a Single Micro-Object in Solution with Femtosecond Laser-Induced Mechanical Force. Appl. Phys. Lett. 2007, 90, 061107. (12) Yan, J.; Skoko, D.; Marko, J. F., Near-Field-Magnetic-Tweezer Manipulation of Single DNA Molecules. Phys. Rev. E 2004, 70, 011905. (13) Lee, H.; Purdon, A. M.; Westervelt, R. M., Manipulation of Biological Cells Using a Microelectromagnet Matrix. Appl. Phys. Lett. 2004, 85, 1063-1065. (14) Frutiger, D. R.; Vollmers, K.; Kratochvil, B. E.; Nelson, B. J., Small, Fast, and under Control: Wireless Resonant Magnetic Micro-Agents. Int. J. Robot. Res. 2010, 29, 613-636. (15) Arabagi, V.; Behkam, B.; Cheung, E.; Sitti, M., Modeling of Stochastic Motion of Bacteria Propelled Spherical Microbeads. J. Appl. Phys. 2011, 109, 114702. (16) Pawashe, C.; Floyd, S.; Diller, E.; Sitti, M., Two-Dimensional Autonomous Microparticle Manipulation Strategies for Magnetic Microrobots in Fluidic Environments. IEEE Trans. Robot. 2012, 28, 467477. (17) Erbil, C.; Yıldız, Y.; Uyanık, N., N-Isopropylacrylamide/Monoalkyl Itaconate Copolymers and N-Isopropylacrylamide/Itaconic Acid/Dimethyl Itaconate Terpolymers. Polym. Adv. Technol. 2009, 20, 926-933. (18) Carias, V.; Wang, J.; Toomey, R., Poly(N-Isopropylacrylamide) Cross-Linked Coatings with Phototunable Swelling. Langmuir 2014, 30, 4105-4110. (19) Klouda, L.; Mikos, A. G., Thermoresponsive Hydrogels in Biomedical Applications. Eur. J. Pharm. Biopharm. 2008, 68, 34-45. (20) Shibayama, M.; Tanaka, T., Volume Phase Transition and Related Phenomena of Polymer Gels. In Responsive Gels: Volume Transitions I, Dušek, K., Ed. Springer Berlin Heidelberg: 1993; Chapter 1, pp 1-62. (21) Kippelen, B.; Marder, S. R.; Hendrickx, E.; Maldonado, J. L.; Guillemet, G.; Volodin, B. L.; Steele, D. D.; Enami, Y.; Sandalphon; Yao, Y. J.; Wang, J. F.; Röckel, H.; Erskine, L.; Peyghambarian, N., Infrared Photorefractive Polymers and Their Applications for Imaging. Science 1998, 279, 54-57. (22) Lowe, A. B.; McCormick, C. L., Synthesis and Solution Properties of Zwitterionic Polymers. Chem. Rev. 2002, 102, 4177-4190. (23) Torres-Lugo, M.; Peppas, N. A., Molecular Design and in Vitro Studies of Novel PH-Sensitive Hydrogels for the Oral Delivery of Calcitonin. Macromolecules 1999, 32, 6646-6651.


Page 7 of 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(24) Shiga, T., Deformation and Viscoelastic Behavior of Polymer Gels in Electric Fields. In Neutron Spin Echo Spectroscopy Viscoelasticity Rheology, Springer Berlin Heidelberg: 1997; Chapter 2, pp 131-163. (25) Xulu, P. M.; Filipcsei, G.; Zrínyi, M., Preparation and Responsive Properties of Magnetically Soft Poly(N-Isopropylacrylamide) Gels. Macromolecules 2000, 33, 1716-1719. (26) DuPont Jr, S. J.; Cates, R. S.; Stroot, P. G.; Toomey, R., SwellingInduced Instabilities in Microscale, Surface-Confined Poly (NIsopropylacryamide) Hydrogels. Soft Matter 2010, 6, 3876-3882. (27) Tirumala, V. R.; Divan, R.; Ocola, L. E.; Mancini, D. C., DirectWrite E-Beam Patterning of Stimuli-Responsive Hydrogel Nanostructures. J. Vac. Sci. Technol., B 2005, 23, 3124. (28) Rubio-Retama, J.; Zafeiropoulos, N. E.; Serafinelli, C.; Rojas-Reyna, R.; Voit, B.; Lopez Cabarcos, E.; Stamm, M., Synthesis and Characterization of Thermosensitive PNIPAM Microgels Covered with Superparamagnetic γ-Fe2O3 Nanoparticles. Langmuir 2007, 23, 1028010285. (29) Stadele, V.; Gasser, U.; Dietsch, H., Ellipsoidal Hybrid Magnetic Microgel Particles with Thermally Tunable Aspect Ratios. Soft Matter 2012, 8, 4427-4431. (30) Purushotham, S.; Chang, P. E. J.; Rumpel, H.; Kee, I. H. C.; Ng, R. T. H.; Chow, P. K. H.; Tan, C. K.; Ramanujan, R. V., Thermoresponsive Core-Shell Magnetic Nanoparticles for Combined Modalities of Cancer Therapy. Nanotechnology 2009, 20, 305101. (31) Satarkar, N. S.; Hilt, J. Z., Magnetic Hydrogel Nanocomposites for Remote Controlled Pulsatile Drug Release. J. Controlled Release 2008, 130, 246-251. (32) Ortega, D.; Pankhurst, Q. A., Magnetic Hyperthermia. In Nanoscience: Volume 1: Nanostructures through Chemistry, O'Brien, P., Ed. Royal Society of Chemistry: Cambridge, 2013, pp 60-86. (33) Binns, C., Magnetic Nanoparticle Hyperthermia Treatment of Tumours. In Nanostructured Materials for Magnetoelectronics, Aktaş, B.; Mikailzade, F., Eds. Springer Berlin Heidelberg: 2013; Chapter 8, pp 197215.

(34) Martinez-Boubeta, C.; Simeonidis, K.; Makridis, A.; Angelakeris, M.; Iglesias, O.; Guardia, P.; Cabot, A.; Yedra, L.; Estrade, S.; Peiro, F.; Saghi, Z.; Midgley, P. A.; Conde-Leboran, I.; Serantes, D.; Baldomir, D., Learning from Nature to Improve the Heat Generation of Iron-Oxide Nanoparticles for Magnetic Hyperthermia Applications. Sci. Rep. 2013, 3, 1652. (35) Khurshid, H.; Alonso, J.; Nemati, Z.; Phan, M. H.; Mukherjee, P.; Fdez-Gubieda, M. L.; Barandiaran, J. M.; Srikanth, H., Anisotropy Effects in Magnetic Hyperthermia: A Comparison between Spherical and Cubic Exchange-Coupled FeO/Fe3O4 Nanoparticles. J. Appl. Phys. 2015, 117, 17A337. (36) Nemati, Z.; Alonso, J.; Martinez, L. M.; Khurshid, H.; Garaio, E.; Garcia, J. A.; Phan, M. H.; Srikanth, H., Enhanced Magnetic Hyperthermia in Iron Oxide Nano-Octopods: Size and Anisotropy Effects. J. Phys. Chem. C 2016, 120, 8370-8379. (37) Khurshid, H.; Chandra, S.; Li, W.; Phan, M. H.; Hadjipanayis, G. C.; Mukherjee, P.; Srikanth, H., Synthesis and Magnetic Properties of Core/Shell FeΟ/Fe3O4 Nano-Octopods. J. Appl. Phys. 2013, 113, 17B508. (38) Castellanos, A.; DuPont, S. J.; Heim, A. J.; Matthews, G.; Stroot, P. G.; Moreno, W.; Toomey, R. G., Size-Exclusion “Capture and Release” Separations Using Surface-Patterned Poly(N-Isopropylacrylamide) Hydrogels. Langmuir 2007, 23, 6391-6395. (39) Akintewe, O. O.; DuPont, S. J.; Elineni, K. K.; Cross, M. C.; Toomey, R. G.; Gallant, N. D., Shape-Changing Hydrogel Surfaces Trigger Rapid Release of Patterned Tissue Modules. Acta Biomater. 2015, 11, 96-103. (40) Brzoska, J. B.; Azouz, I. B.; Rondelez, F., Silanization of Solid Substrates: A Step toward Reproducibility. Langmuir 1994, 10, 43674373. (41) Andreu, I.; Natividad, E., Accuracy of Available Methods for Quantifying the Heat Power Generation of Nanoparticles for Magnetic Hyperthermia. Int. J. Hyperthermia 2013, 29, 739-751. (42) Mora, T.; Boudaoud, A., Buckling of Swelling Gels. Eur. Phys. J. E 2006, 20, 119-124.

TABLE OF CONTENTS (TOC) Graphic


Remotely Controlled Micromanipulation by ... - ACS Publications

Recommend Documents